Well as has been pointed out, the objectives of OVERLORD were quite a lot more ambitious than those of SEALION, so a lot more resources had to be thrown at it. The Sealion forces only had to go 40 miles or so to get to London; the Overlord forces had to travel hundreds of miles to get to Berlin. The Overlord forces were much much bigger than the Sealion forces and the opposition to the Sealion forces much weaker - Sealion faced much weaker defences, even the stop lines (including the GHQ line) were only two pill boxes deep. In September 1940 there were only the equivalent of a couple of inexperienced, under-equipped, poorly trained and poorly generaled divisions defending beaches "B" - "E". I would expect a different situation in May 1941 however.Neptune also has a massive naval presence, 7 BBs, 5 CA, 17 CL, 135 DD and DE, and over 500 other warships. At this point Germany's entire fleet could match the CL and up numbers the allies brought to bear.
Yes, the British destroyer and destroyer escort force alone had increased by about 60 ships by May 1941 but that didn't stop the period after September 1940 (until March or April 1941) from being part of the first U-boat "happy time". Since there were sufficient ships guarding home waters, most if not all that increase would have gone to the Atlantic or overseas. Even so, there remained a huge disparity in numbers between the Nazi and British navies, and that's what makes it all interesting, seeing if this can somehow be overcome.
Oh, and lets not forget a well played deception based on controlling any information the enemy gets about you, while you are in fact quite well informed about them.
Well the Germans had broken the British naval and meteorological cyphers so they had weather reports from the Atlantic and knew quite a bit about British naval operations. Their knowledge of British land forces was not wholly accurate, but it was an over-estimate so their planning had some cushioning in it. They had pretty good maps of the British fortifications and of Britain in general (including geotechnical maps). The British had good control over their information but didn't know the German intentions exactly, as can be shown by the location of the GHQ reserve - it was placed so it could travel to the east coast if necessary. It's also shown by the announcement of "Cromwell" ("invasion immanent") when no invasion was in the offing.
That assumes that full production hasn't been reached and a BOB mark 2 will be fought in exactly the same way as Mark 1. If the Germans are successful to begin with, then they will experience a declining loss rate as the battle proceeds and British numbers decline, while British losses increase, so a longer battle will benefit them. Although British numbers have increased and continue to increase, the Germans still have an advantage in the number of experienced pilots.A longer BoB means more shadow factories can be brought into play, offsetting the lost production of known factories. Also, Germany is losing numbers too, both in pilots and in serviceable aircraft, so a longer Battle only works more in Britain's favour.
Well they had to struggle to be recognised by the British as something better than monkeys and there aren't any replacements for those pilots from their own countries.Before that is was Allied (French, Czech, Polish, etc.) pilots, to such a degree that the British had more active pilots by the time the BoB was over than they'd started with, while the Germans had fewer.
So you don't know how many there were, either. Some/lots were definitely sent to Malta, Malaya, and Egypt. They had a significant effect on German and Italian forces in North Africa in 1941.No, Malta wasn't being bombed, and the Italians were held at bay by their own weaknesses.